How to create a custom EL function to invoke a static method?

Solution 1:

First create a final class with a public static method which does exactly the job you want:

package com.example;

import java.util.Collection;

public final class Functions {

    private Functions() {
        // Hide constructor.
    }

    public static boolean contains(Collection<Object> collection, Object item) {
        return collection.contains(item);
    }

}

Then define it as a facelet-taglib in /WEB-INF/functions.taglib.xml:

<?xml version="1.0" encoding="UTF-8"?>
<facelet-taglib 
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facelettaglibrary_2_0.xsd"
    version="2.0">
    <namespace>http://example.com/functions</namespace>

    <function>
        <function-name>contains</function-name>
        <function-class>com.example.Functions</function-class>
        <function-signature>boolean contains(java.util.Collection, java.lang.Object)</function-signature>
    </function>
</facelet-taglib>

Then familarize Facelets with the new taglib in the existing /WEB-INF/web.xml:

<context-param>
    <param-name>javax.faces.FACELETS_LIBRARIES</param-name>
    <param-value>/WEB-INF/functions.taglib.xml</param-value>
</context-param>

(note: if you already have the javax.faces.FACELETS_LIBRARIES definied, then you can just add the new path semicolon separated)

Then define it in the Facelets XHTML file as new XML namespace:

<html 
    xmlns="http://www.w3.org/1999/xhtml"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:func="http://example.com/functions"
    ...
>

Finally you can use it as intended:

rendered="#{func:contains(bean.panels, 'u1')}"

As a completely different alternative, you can also include JBoss EL in your project. It works on Tomcat 6.0 and you'll be able to invoke non-getter methods in EL. Drop jboss-el.jar file in /WEB-INF/lib and add the following to your web.xml:

<context-param>     
    <param-name>com.sun.faces.expressionFactory</param-name>
    <param-value>org.jboss.el.ExpressionFactoryImpl</param-value>   
</context-param>

Since EL 2.2 there's another approach: create an @ApplicationScoped bean with methods in turn referring to those static functions. See also a.o. Utility methods in application scoped bean.

How to create a custom EL function to invoke a static method?

Solution 1:

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